Methods of x-ray diffraction, electron microscopy and optical diffraction are being used to study the structure and action of three multisubunit enzymes: aldolase from rabbit muscle, glutamine synthetase from E. coli, and ribulose-bisphosphate carboxylase from tobacco. The regulation of transcription of genes coding for enzymes of nitrogen metabolism by glutamine synthetase is being studied by electron microscopy and in vitro biochemical methods.